A selective-fire firearm has at least two firearm modes, which are activated by means of a selector which varies depending on the weapon's design. Some selective-fire weapons have burst fire mechanisms to limit the maximum number of shots fired automatically in this mode. The most common limits are two or three rounds per trigger pull. Fully automatic fire refers to the ability for a weapon to fire continuously until the feeding mechanism is either emptied or the trigger is released. Semi-automatic refers to the ability to fire one round per trigger pull.